1. Field of the Invention
The present invention relates to a root wrapping type aseismic reinforcement construction and method for a base of a column member.
2. Description of Related Art
Various aseismic reinforcement methods for increasing resistance to earthquake have been studied on existing buildings, civil engineering structures, and other structures, which were built in conformity with the old seismic design standards, by making good use of our experience in great earthquakes gained by, for example, superhighways destroyed by the Great Hanshin Earthquake and by assuming a case where an earthquake greater than the previous one occurs. For example, as an aseismic reinforcement method for steel framed reinforced concrete structures, there have been proposed a method in which reinforcing bars are wrapped around a column member and concrete is placed to increase the resistance of the column member, a method in which a steel plate is wrapped around a column member, and a method in which a carbon fiber sheet or the like is wrapped around the whole outer peripheral surface of a column, which has been disclosed in Japanese Patent Provisional Publication No. 11-117541 (No. 117541/1999).
For plant structures such as liquefied natural gas (LNG) storing facilities, although the plant structures were not damaged fatally by the Great Hanshin Earthquake, there occurred damage such as broken pipelines for energy transportation and dropped beds for supporting the pipelines. Therefore, a review of seismic diagnosis for a column base of a bed for piping system has been made, and an aseismic reinforcement method therefor has been studied.
In this case, various methods are possible as a method for improving a column member of an existing structure to provide an aseismic reinforcement construction. For example, a method in which a column base and foundation are reinforced extensively is possible. However, the aseismic reinforcement of foundation has a disadvantage that the work is complicated, so that a long term of work and a high cost are required.
On the other hand, a method in which a column base etc. exposed above the ground are reinforced without the extensive reinforcement of foundation has an advantage that necessary and sufficient earthquake-resistant performance can be provided, and the work is simple, so that the work can be performed in a short period of time.
As an example of this aseismic reinforcement method, Japanese Patent Provisional Publication No. 10-331437 (No. 331437/1998) has disclosed a method in which a reinforcement metal is joined at a position where an existing beam and column are joined on a steel column of an existing steel structure to increase the shearing strength and bending strength of the beam-column joint.
Also, Japanese Patent Provisional Publication No. 10-18424 (No. 18424/1998) has disclosed a method in which reinforced concrete is wrapped in the vicinity of the lower end of a steel column as a reinforcement method for a steel column base on a structure for connecting the steel column to the foundation.
The following is summarization of problems arising when the concept of the above-described aseismic reinforcement method for a column base is applied to a bed for piping system with a construction in which one steel column member is arranged on one pile foundation.
The conventional concept of the aseismic reinforcement for a bed for piping system is that letting a be the stress applied to the foundation by a seismic force, f be the allowable stress of foundation, and "sgr"/f be the allowable unit stress, a column and a beam are reinforced with a cover plate so that the allowable unit stress ("sgr"/f) obtained by the cross-section calculation is lower than 1, by which the rigidity is increased so that the structure can withstand a seismic force exceeding that at the time of design.
On the other hand, the aseismic reinforcement of a column base has been effected by wrapping reinforced concrete around the base to reduce an effect on the foundation and to prevent a base plate from buckling. The design concept for the column base of the bed for piping system is as described below, assuming that the method for supporting the column base by means of the foundation is premised on a pin condition.
Specifically, 1) an anchor bolt connecting the steel column base to the foundation bears an axial force and shearing force, 2) the foundation member bears an axial force from the anchor bolt and bending moment caused by the shearing force, and 3) the base plate bears a tensile force and bending moment caused by the anchor bolt and pushing and withdrawing caused by the column.
Therefore, if the steel column base is rigidly connected to the foundation by joining the reinforcement metal to the beam-column joint at the lower end of the steel column or by wrapping reinforced concrete as the reinforcement method for the steel column base, the method for supporting the column base by means of the foundation changes from the pin condition to a fixed condition, so that the shearing force and bending moment are transmitted to the foundation via an interface at which the reinforcement metal or the reinforced concrete comes newly into contact with the column base. Since the shearing force and bending moment transmitted to the foundation increase in correlation with the magnitude of the seismic force when the seismic force increases, in the case where the steel column base is rigidly connected to the foundation, if the allowable unit stress is exceeded, the foundation itself cannot withstand the stress, and may be broken.
In the conventional foundation strength design, however, although a sufficient safety factor for the axial force is secured, the safety factor for the bending moment actually does not have an enough margin as compared with that for the axial force. Therefore, it is found that although the aseismic reinforcement in which the cover plate is put on the column and beam is suitable for the case where the allowable stress of the foundation has some degree of margin, the aseismic reinforcement in which the column and beam are simply reinforced with the cover plate is unsuitable for the case where design is made so that the allowable stress of the foundation has a small margin.
The present invention has been made to solve the above problems with the related arts, and accordingly an object thereof is to provide a root wrapping type aseismic reinforcement construction and method in which a buffering portion is provided between a base of a column member and a root wrapping member to decrease bending moment generated on the base by an external force, and therefore the bending moment is less prone to be transmitted to a foundation member, so that the bending moment born by the foundation member can be reduced.
To achieve the above object, the root wrapping type aseismic reinforcement construction in accordance with the present invention is configured as described below. Specifically, the root wrapping type aseismic reinforcement construction in which a base of a column member erected on a foundation member is reinforced with a root wrapping member comprises a buffering portion provided between the base of the column member and the root wrapping member.
Preferably, the buffering portion is a clearance provided between the column base and the root wrapping member.
Preferably, the buffering portion is a clearance provided between the column base and the root wrapping member and further filled with a filler.
Preferably, the root wrapping member and the filler regulate bending moment generated when the column member is deformed.
Preferably, the filler is either an elastically deformed material including vibration proof rubber or an elastic element including a spring.
Preferably, the filler is either a plastically deformed material including either a metallic material or a metallic alloy or a plastically deformed structural element.
Preferably, the root wrapping member is a reinforced concrete root wrapping member formed by placing reinforced bars at the outer periphery of the column base and the upper end portion of the foundation member, by placing outer winding hoops at the outer periphery of the reinforcing bars, and by placing concrete in a space within the outer winding hoops.
Preferably, a bend constraining force caused on the column base by an external force is relieved, and bending moment generated on the column base is regulated, thereby reinforcing the foundation member.
Also, the root wrapping type aseismic reinforcement method in accordance with the present invention comprises the steps as described below. Specifically, the root wrapping type aseismic reinforcement method in which a base of a column member erected on a foundation member is reinforced with a root wrapping member comprises a buffering step of regulating bending moment generated on the base of the column member by the application of an external force to the column member at a portion between the base and the root wrapping member, and a regulating step of further regulating the bending moment by absorbing the bending moment regulated in the buffering step.
Also, according to the present invention, the root wrapping type aseismic reinforcement method in which a base of a column member erected on a foundation member is reinforced with a root wrapping member comprises a clearance forming material providing step of providing a forming material for forming a clearance at the outer periphery of the base facing the root wrapping member; a fixing step of placing reinforcing bars at the outer periphery ranging from the base of the column member to the upper end portion of the foundation member, placing outer winding hoops at the outer periphery of the reinforcing bars, and fixing the reinforcing bars to the upper end portion of the foundation member; a member forming step of placing concrete in a space within the outer winding reinforcing bars fixed in the fixing step to form a reinforced concrete root wrapping member, including the forming material provided in the clearance forming material providing step; and a clearance forming step of forming a clearance by removing the forming material from the reinforced concrete root wrapping member formed in the member forming step.
Preferably, the root wrapping type aseismic reinforcement method further comprises a filling step of filling the clearance formed in the clearance forming step with a filler.
As described above, according to the root wrapping type aseismic reinforcement construction and method for the column member erected on the foundation member in accordance with the present invention, the buffering portion is provided between the base of the column member and the root wrapping member to decrease the bending moment generated on the base by an external force, and therefore the bending moment is less prone to be transmitted to the foundation member, so that the bending moment born by the foundation member can be reduced.